This application claims the priority of German Patent Application, Serial No. 10114321.4, filed Mar. 23, 2001, the subject matter of which is incorporated herein by reference.
The present invention relates to an electric machine of a type having a stator with laminated stator body, rotor and potted winding end portions.
European Pat. No. EP 0 915 554 A2 describes an electric motor which includes a stator without housing and with a laminated stator body of rotation-symmetric configuration. The stator body has cooling slots which are located on the slot-distal side of the stator body and receive cooling conduits for conduction of a cooling medium. Winding end portions axially extend out of the stator, whereby a heat-conducting plastic material connects the cooling conduits with the stator body and the winding end portions.
This electric motor suffers shortcomings because the cooling conduits are connected with the winding end portions by a heat-conducting plastic casting material in a single operation. This has to be taken into account during fabrication. Before casting, the cooling conduits may be slightly damaged. Furthermore, the cooling device is used for cooling the laminated stator body as well as for the winding end portions. This lack of discrimination is disadvantageous because it fails to take into account the desired increased need for heat dissipation in the area of the winding end portions.
It would therefore be desirable and advantageous to provide an improved electric machine to obviate prior art shortcomings and to enhance a cooling of the winding end portions while yet simplifying fabrication.
According to one aspect of the present invention, an electric machine, includes a stator with a laminated stator body having winding end portions encased in a casting material that forms a cast, a rotor for interaction with the stator, and an arrangement for carrying away heat generated by the electric machine, with the arrangement including surface-enlarging structures formed on the surface of the cast and/or a heat-conducting envelope which is, at least partially, provided upon the cast.
Surface-enlarging structures in the cast material of the winding end portions enhance a cooling of the winding end portions and improve the heat dissipation. This is realized through passive cooling by means of convection and/or active cooling by means of gaseous or liquid cooling media, which carry off heat though their volume flow. In addition, enclosing the cast for the winding end portion with a heat-conducting envelope can further enhance cooling of the winding end portion.
Further advantageous configurations for providing an improved cooling of the winding end portion through a heat-conducting encasement may be realized through combination of surface-enlarging structures with a heat-conducting envelope of winding end portions. Heat-conducting envelopes of potted winding end portions bear at least partially upon the casting material. The heat-conducting envelope is made of a highly heat-conducting material which, unlike the heat-conducting casting material, may also be electrically conducting. Examples of highly heat-conducting material include in particular metals, such as copper, aluminum or iron, or metal alloys.
Heat-conducting envelopes are capable to direct heat from regions that are difficult to reach by active coolants, such as gases and/or liquid, to regions that are more accessible. For example, heat can be carried away from the zone of the inner radius area of the potted winding end portion or also from the region at the end face of the potted winding end portions. Establishing a contact of the envelope with a cooling fluid can optimize heat dissipation by means of a heat-conducting envelope. With air-cooling, the heat dissipation is suitably implemented by a combination of cooling air stream and cooling body. In the event, cooling with liquid is desired, the heat-conducting envelope should have contact with a liquid-cooled body.
Surface-enlarging structures should be so configured as to allow the fabrication of a negative mold as well as a positive moldxe2x80x94negative impression and positive impressionxe2x80x94that can easily be fabricated. Preferred are wavy, triangular, pyramid-like structures or combinations thereof. Mold design requirements should hereby be taken into account.
Suitably, the electric machine is provided with laminated stator body, rotor, potted winding end portions formed by conductors, and casting material with cooling channels for conduction of a coolant, whereby the cooling medium absorbs heat from the winding end portions, with the heat being carried away across surface-enlarging structures of the cast. The surface-enlarging structures may be of the macroscopic type as well as microscopic type. Crucial is only the heat-conducting contact area. In the event, cooling channels are disposed in a cooling jacket or in cooling slots of a laminated stator body, a surface-enlarging structure may be implemented by the cooling jacket itself or by the material which forms the cooling slots.
According to another feature of the present invention, the overall cooling system is so configured as to provide a higher degree of cooling of the winding end portions compared to the cooling of the stator body. Such a targeted or discriminating cooling action takes into account different temperature development in the winding end portions, i.e. in the zone, of the winding end portions, and in the zone of the stator body. In particular, when highly exploited indirect water-cooled machines are involved, the temperature at the winding end portions is substantially higher than the temperature in the stator body, thereby forming the basis for the recognition to provide a better cooling action in the area of the winding end portions. An enhanced cooling action may be realized through denser, i.e. closer, arrangement of cooling channels. Moreover, the cooling channels may not only be arranged two-dimensional in a plane in side-by-side disposition but can also be arranged three-dimensional in staggered disposition. As a consequence of the increased cooling action in the area of the winding end portions, an uneven heat distribution is offset and the motor can be better exploited according to the thermal classes. Example of cooling systems include air cooling, liquid cooling or gas cooling, which can each be suited to the requirements at hand.
Another feature of the present invention involves the utilization of heat-conducting envelopes for heat transport and improved cooling of the winding end portions. Heat-conducting envelopes of potted winding end portions bear at least partially upon the cast, and may be made of a highly heat-conducting material, which unlike the heat-conducting casting material may also be electrically conducting. Examples include in particular metals, such as copper, aluminum or iron, or metal alloys.
Heat-conducting envelopes are capable to guide heat from regions that are difficult to reach by active coolants, such as gases and/or liquid, to regions that are more accessible. For example, heat can be carried away from the zone of the inner radius area of the potted winding end portion or also from the region at the end face of the potted winding end portions. The heat conduction is routed to conventional cooling devices such as air-cooling or liquid cooling.
The heat transport by means of a heat-conducting envelope can be optimized through contact of the envelope with a cooling assembly. Examples of a cooling assembly include the cooling jacket or the formed part having the cooling slots in which the cooling channels, e.g. cooling conduits, are incorporated.
Just as the cast for encasing the winding end portions may have surface-enlarging structures, it is also conceivable to provide the heat-conducting envelope with surface-enlarging structures. The configuration of such surface-enlarging structures can be best suited to the type and scope of the cooling action and in particular can be shaped in dependence on the desired cooling action. In particular, when active cooling is involved, e.g., cooling air flow or cooling water, the heat-conducting envelope may be formed with surface-enlarging structures such as wavy profiles, wedged profiles or combinations thereof.
When taking into account the different heat fluxes to be carried away, the components for conducting the heat flow may have a cross section that is sized in dependence with the magnitude of the heat flow to be carried off. In the event, a heat-conducting envelope is routed across the inner radius of the casting material and contacts the end face of the cast, the heat flow to be carried off is increased.
Suitably, the heat flow to be carried off is guided in the enlarged cross section of the components to a cooling assembly. As a consequence of the greater cross sectional area, a greater contact area can be established with an active component of the cooling system or active component for cooling, such as a cooling jacket.